A number of methods are known in the art for measuring the concentration of specific ions in solution. One method involves introducing a reagent into a sample solution to thereby form a precipitate with the ion whose concentration is to be measured. The precipitate is separated from the solution, dried, weighed, and then the amount of the ion is calculated based on the amount of precipitate formed. This method is cumbersome and time consuming, however, and requires essentially nonportable equipment such as an accurage weighing apparatus.
Another method is illustrated in U.S. Pat. No. 2,880,071, issued Mar. 31, 1959 to Gelman. The method employed comprises measuring the conductivity of the solution. U.S. Pat. No. 4,002,428, issued Jan. 11, 1977 to Blanchard, also employs conductivity measurements as well as pH measurements and the addition of a reagent capable of reacting with the desired ion to get a substantially non-ionic product. Briefly, the process disclosed in U.S. Pat. No. 4,002,428 comprises first measuring the pH and specific conductivity of the sample solution and of a reagent solution. The process then adds and reacts the measured excess amount of the reagent solution with the sample solution thereby allowing the reagent solution to react with the desired ion to get a substantially non-ionic product without a substantial reaction taking place between the reagent solution and the other ions in the solution. The pH and specific conductivity of the resultant mixture is then measured and the concentration of the desired ion mathematically deduced by comparing the specific conductivity expected in the mixture of the sample solution and the reagent solution, assuming no reaction had taken place, with the measured specific conductivity for the solution obtained upon mixing the two solutions and by making any necessary corrections for pH changes and for the solubility of the product of reaction between the desired ion and the reagent solution. Such methods can be somewhat time consuming and are only really applicable in a batch-type method upon taking a sample of the solution to be measured.
Another method is disclosed in U.S. Pat. No. 3,591,481, issued July 6, 1971 to Riseman. The method employs an ion specific electrode. In this method concentration measurements are effected by relating the electrode potential resulting from an unknown or sample solution with the electrode potential from a mixture of that sample solution with a standard solution of known concentration of the ion of interest or a strong complexing or precipitating agent for the ion of interest. The method of obtaining a measurement requires two essential steps. First, the electrode sensitive to the ion of interest is immersed into a specific volume (e.g., 50 ml) of the sample solution containing an unknown amount of the ion of interest; the potential developed then causes a deflection of a meter movement in accordance with the Nernst equation. The meter movement is then adjusted to a null point and small known volume (e.g., 1 ml) of a standard solution containing a known concentration of the ion of interest (or a strong complexing or precipitating agent therefor) is added to the sample. The addition of the standard solution will change the total so that a new potential will arise which causes the meter movement to deflect away from the null point by some value .DELTA.E. Since the concentration of the standard solution is predetermined, the concentration of the sample will appear as a reading on the meter scale or base expressed typically in moles per liter based on the value of .DELTA.E.
The method of the present invention, however, provides an alternative method for measuring the concentration of the specific ion in solution which employs ion exchange resins as well as ion specific electrodes. The present invention exhibits advantages over current analysis methods in that the method is suitable for use in continuous flow systems, is more sensitive than currently available methods, and is more rapid than current methods.
Accordingly, it is an object of this invention to provide a novel process and apparatus for determining the concentration of an ion in solution.
Another object of this invention is to provide a method for determining the concentration of an ion in solution which is suitable for use in continuous flow systems.
Still another object of this invention is to provide a method which is more sensitive and more rapid than currently available methods for determining the concentration of an ion in solution.
Other aspects, objects, and advantages of the present invention will become apparent from a study of the disclosure, the appended claims, and the drawing.